1. Field of the Invention
This invention relates to a pressure detector and a strain member therefor, and more particularly to a pressure detector which uses a special strain member. The strain member is rectangular and has windows formed between its opposing edge surfaces which are held stationary, so that when a force is applied to the strain member at a position between the opposing edge surfaces in parallel thereto the windows flex depending on the force thus applied. The pressure detector of the invention is particularly suitable for accurate pressure detection in an apparatus to be run at a high temperature, such as an internal combustion engine and a fluid processing plant like a food processing plant, over a wide temperature range in special surroundings, e.g., in a bacteriologically clean environment.
2. Description of the Prior Art
In food processing plants and automobile factories, there is an increasing demand for accurate measurement of the pressure under special conditions; namely, that that surface of the pressure detector which is to be in contact with fluid being measured must be flat and must be kept sufficiently clean for completely eliminating any bacteriological proliferation, and that accurate measurement must be ensured at a comparatively high temperature such as at 150.degree. C.
In a typical pressure detector of the prior art as shown in FIG. 1, a flexible diaphragm 81 is fastened to a fixed member 82 in such a manner that a pressure-receiving portion 83 of the diaphragm 81 flexes in proportion to a pressure applied thereto. The deflection of the pressure-receiving portion 83 is transmitted to the free end of a cantilever type strain member 85 through a coupling means 84. The opposite end of the strain member 85 is fastened to a fixed member 82a, and a pair of strain-sensitive elements 86a and 86bare mounted on opposing surfaces of the strain member 85 in the proximity of the fastened end thereof.
The strain-sensitive elements 86a and 86b are made of metallic wires or semiconductors, and electric output signals from the strain-sensitive elements 86a and 86b indicate the deflection of the strain member 85 and hence the magnitude of the pressure acting on the pressure-receiving portion 83 of the diaphragm 81. Thus, the fluid pressure is converted into the deflection of the strain member 85 and then detected in the form of the above electric signals from the strain-sensitive elements 86a and 86b.
The pressure detector of the prior art as shown in FIG. 1, however, has shortcomings in that the surface of the flexible diaphragm 81 is uneven with recessed portions where solid material is likely to be precipitated in a hardly removable manner so as to make it difficult to maintain high accuracy and bacteriological cleanness, and that the temperature of the fluid being measured is easily transmitted to the strain member 85, resulting in an increased temperature error in the measurement.
Besides, the cantilever type strain member 85 of the prior art has a number of shortcomings; namely, that coupling portions and parts (not shown) which join the fastened end of strain member 85 to the fixed member 82a are susceptible to slight strain due to the flexing of the strain member 85 resulting in a measurement error; that, if the above-mentioned coupling portions and parts are made sturdy enough to prevent any strain thereat, they become bulky and miniaturization becomes difficult; that, when the strain member 85 is made of metallic material to withstand mechanical loading, the difference in thermal expansion between the metallic strain member 85 and the strain-sensitive elements 86a, 86b tends to cause a measurement error; and that, when an organic adhesive is used to join the strain sensitive elements 86a, 86b to the strain member 85 so as to make up for the difference in thermal expansion therebetween, the organic adhesive tends to cause a measurement error.